Currently known flippers comprise especially a bootee and a wing section. The bootee can be closed or open at the rear, the foot in this case being held in said open bootee by means of a strap supported on the heel. The wing section extends to the front of the bootee to which it is secured.
During swimming, that is, during an upward movement and a downward movement of the flipper corresponding to flapping of the feet, the wing section flexes respectively downwards and upwards. During the descent phase, the knee extends and the hip flexes, while inversely during the ascent phase the knee flexes and the hip extends; the swimmer has more power during the descent phase than the ascent phase. A major drawback to currently known flippers is not exploiting this variation in power during flapping of feet, given that the wing section flexes identically in one direction or in the other during flapping of the feet, that is, the wing section flexes symmetrically.
Document FR 1 361 410 is known which discloses a flipper whereof the aim is to be able to vary the flexibility of the wing section. To achieve this, longitudinal conduits are arranged on the underside of the wing section, which allow introduction of stiffening rods. Such a design ably replaces rods by other more or less flexible rods, helping to vary the flexibility of the wing section. This design however ensures symmetrical flexing of the wing section during flapping of the feet during swimming.
Document DE 4 338 610 is also known which discloses a flipper comprising a bootee, a wing section and two flexible elements fixed to the bootee and extending to the front of the flipper, respectively above and below the wing section. As a function of the flexibility of each of the two flexible elements this produces asymmetrical flexing of the wing section during descent and ascent movement of the flipper during swimming.